A first stage of a power supply circuit of an electrical household appliance is constructed from an AC/DC converter circuit converting an AC (alternating current) voltage to a DC (direct current) voltage. In this converter circuit, a PFC circuit is provided for reducing reactive power and a harmonic noise. In order that size reduction, height reduction, or the like may be achieved in a choke employed in the circuit, the core employed in this is required to have a high saturation magnetic flux density, a low core loss, and an excellent direct-current superposing characteristic (a high incremental permeability).
Further, in an electric power unit mounted on an electric-motor driven vehicle such as a hybrid vehicle whose rapid spreading has begun in recent years, on a photovoltaic power generation apparatus, or on the like, a reactor tolerant of high currents is employed. Also in the core for such a reactor, a high saturation magnetic flux density is similarly required.
For the purpose of satisfying the above-described requirement, a metal powder core is adopted that has a satisfactory balance between the high saturation magnetic flux density and the low loss. For example, the metal powder core is obtained by employing soft magnetic powder of Fe—Si—Al-based, Fe—Si-based, or the like and then performing forming after performing insulation treatment on the surface thereof. Thus, electric resistance is improved by the insulation treatment so that eddy current loss is suppressed.
As a technique relevant to this, International Publication No. 2010/084812 proposes a metal powder core employing: first magnetic atomized powder; and second magnetic atomized powder having a smaller grain diameter than that. Composite magnetic powder in which the surface of the first magnetic atomized powder is covered by the second magnetic atomized particles by using a binder is formed and then pressure forming is performed on this so that a metal powder core is obtained in which the density is improved and the eddy current loss is suppressed. Further, paragraph [0029] in International Publication No. 2010/084812 describes that as an embodiment, powder or the like such as copper powder may further be employed. However, it does not describe what kind of operation effect is caused by the powder or the like such as copper powder. Here, for example, the first and the second magnetic atomized powder are composed of a soft magnetic material such as iron (Fe), an iron (Fe)-silicon (Si)-based alloy, an iron (Fe)-aluminum (Al)-based alloy, an iron (Fe)-nitrogen (N)-based alloy, an iron (Fe)-nickel (Ni)-based alloy, an iron (Fe)-carbon (C)-based alloy, an iron (Fe)-boron (B)-based alloy, an iron (Fe)-cobalt (Co)-based alloy, an iron (Fe)-phosphorus (P)-based alloy, an iron (Fe)-nickel (Ni)-cobalt (Co)-based alloy, and an iron (Fe)-aluminum (Al)-silicon (Si)-based alloy.
Japanese Patent Application Laid-Open No. H10-208923 proposes a metal powder core obtained such that a mixture containing: a soft magnetic material such as pure iron, an Fe—Si—Al-based material, an Fe—Si-based material, permalloy, and permendur; at least one or more kinds selected from Fe, Al, Ti, Sn, Si, Mn, Ta, Zr, Ca, and Zn serving as A-group metals; and one or more kinds selected from oxides B (oxides having a higher oxide generation energy than the A-group metals); is pressed and then heat treatment is performed at 500 degrees C. or higher. When one having a high ductility is employed as the A-group metal, at the time that it is mixed with the magnetic material and then pressed, the A-group metal suffers plastic deformation so that the compacting pressure is allowed to be reduced and hence the strain in the magnetic material is also reduced so that the hysteresis loss is reduced. The oxides B having a higher oxide generation energy than the A-group metals are oxides such as Cu, Bi, and V.
International Publication No. 2009/139368 proposes a metal powder core in which an Fe-based amorphous alloy is employed as a magnetic material for the purpose of further core loss reduction, strength improvement, and the like. Pulverized powder of Fe-based amorphous alloy ribbon and atomized powder of Fe-based amorphous alloy containing Cr are employed as main components and then the grain diameters and the mixing ratio of these are set forth so that the compaction density is improved. By virtue of this, a low core loss and an excellent direct-current superposing characteristic are obtained which are the features of Fe-based amorphous alloy ribbon.